The M3 is a one space rack mount unit designed to be the main monitor control for a digital audio workstation or a computer based video editing system. It has 4 balanced stereo inputs selectable from the source switch. A high quality balanced level control feeds the Alt Speaker switch which selects one of three stereo outputs to feed to powered monitors or amplifiers. There are left and right mute switches and a mono compatable switch to check for phase discrepancies. The main signal path is passive except when the mono switch is used a summing amp is inserted to give a true mono output. All inputs and outputs are on XLR connectors.